Direct lighting luminaires



Oct.;8, 1957 K. FRANCK Re. 24,372

DIRECT LIGHTING LUMINAIRES Original Filed Feb. 1, 1952 4 Sh eets-Sheet 1I V I 9/ ATTORNEY Oct. 8, 1957 K FRANCK DIRECT LIGHTING LUMINAIRES 4Sheets-Sheet Original Filed Feb. 1, 1952 R T N V E V m .Y E N m M am k ANm Oct. 8, 1957 FRANCK Re 24,372

DIRECT LQGHTING LUMINAIRES Original Filed Feb. 1, 1952 A 4 Sheets$heqt 33, 1957 K. FRANCK Re. 24,372

DIRECT LIGHTING LUMINAIRES Original Filed Feb. 1; 1952 4 Sheets-Sheet 4era 5 ATTURWE Y United States Patent ()fifice Re. 24,372 Reissuecl Oct.8, 1957 DIRECT LIGHTING LUMINAIRES Kurt Franck, Newark, Ohio, assignorto Holophane Company, Inc., New York, N. Y., a corporation of DelawareOriginal No. 2,756,326, dated July 24, 1956, Serial No. 269,517,February 1, 1952. Application for reissue December 28, 1956, Serial No.631,387

28 Claims. (Cl. 240-93) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

The present invention relates to direct lighting luminaires, and is moreparticularly directed toward direct lighting luminaires adapted forrelatively low mounting heights above the working areas.

In such fixtures, the screening of the light source itself and ofsources of annoying brightness in the glare zones is extremely importantand it is necessary to concentrate the output into angles from nadirwhich suitably light horizontal and vertical surfaces at usual ratios ofspacing to mounting height.

The present invention contemplates luminaires for these purposesemploying with the light source a specular reflector closed ofl? by aprismatic light transmitting plate adapted to cooperate to veryefficiently transmit the light from the source and place it on theworking area and to have very desirable brightness and appearancecharacteristics.

Other and further objects will appear as the description proceeds.

The accompanying drawings show, for purposes of illustrating the presentinvention, one embodiment in which the invention may take form, togetherwith modifications of certain parts, it being understood that thedrawings are illustrative of the invention rather than limiting thesame.

In the accompanying drawings:

Figure 1 is a transverse vertical section taken at a relatively smallscale through a direct lighting luminaire, showing in full lines theprofiles of the reflector and refracting plate and the paths of directand reflected rays from a source at a point in said plane, and showingin dotted lines the diagonal profiles of a square luminaire and lightcontrol in diagonal planes from such a source, the full line sectionbeing on the line 1--1 of the square fixture of Figure 2, the dottedline section being on the diagonal of Figure 2.

Figure 1a is a fragmentary view similar to Figure 1 but at an enlargedscale to show light control at the margins of the reflector and plate;

Figures 1b and 1c are fragmentary sectional views at a larger scale,illustrating the lamp box and trim which support the reflector andrefracting plate;

Figure 2 is a top plan view of a square fixture taken on the broken line2-2 of Figure I;

Figure 3 is a top plan view of one-quarter of the square refractingplate of Figures 1 and 2;

the square plate taken in the plane 1-1 of Figure 2 and on the diagonal;

Figures 6 and 7 are diagrammatic views illustrating in plan and sectionthe geometric layout to obtain the three dimensional contours of themolding equipment and the resulting refractor; 7

Figures 8 and 8a are fragmentary sectional views taken respectivelythrough the improved and prior art refracting prisms to show comparisonof light control;

Figure 9 is a perspective view of the square refract ing plate as viewedfrom underneath and in an oblique direction and showing the curvature oftypical prisms;

Figure 9a is a photograph of the plate similarly viewed;

Figure 10 is an inverted plan view of a refracting plate suitable foruse at the end of an elongated direct lighting fixture; and

Figure 11 is a fragmentary inverted plan view of a modified form of lensplate.

The luminaire of Figures 1 to 2, inclusive, is shown as a squareluminaire adapted to employ a square lamp box and to be recessed intothe ceiling so that only the light transmitting plate and trim arevisible.

The lamp box 20 made of sheet metal is received into the usual plasterflange 20a and is of the proper size to accommodate the parts. It has anarrow external flange 21 to engage the ceiling and inner flanges 22 tosupport the opposite edges of the reflector. A tens frame 23 is held innormal closed position by nonremovable nuts 24 threaded on bolts 25extending down from the sides of the box and when the luminaire is open,the lens frame is suspended from a loop 26. The opening in the lensframe is just slightly smaller than the box, and very narrow trimsuflices to support the lens and cover the joint between the ceilingsurfacing and the lamp box.

The lamp box carries a diagonal bracket 27 in an upper side corner, andthis supports the lamp socket 28 and lamp 29 on an oblique axis. Thelamp filament F is centered and at the proper distance above the mouthof the lamp box.

The reflector 30 for use with a concentrated filament source ispreferably a prismatic glass reflector to withstand the heat and has arectangular mouth whose side edges or flanges rest on the box-carriedflanges 22. The preferred cut-off angle is 50 above the nadir. Thereflector is apertured at 32 to accommodate the lamp 29.

As shown, the reflector 30 is symmetrical about a normally verticalmedian plane XX. It has upwardly and inwardly converging sides 33, 33 ofpyramidal shape and is provided with a dome-like top 34. The sides havevertical totally reflecting prisms 33a. The top has horizontal annularand vertical totally reflecting prisms 34a, 34b, respectively, alsoinner refracting prisms 340. The transition from annular tosquare-shaped may be stepped as indicated in Figure 2 or mergingsurfaces may be employed.

Light rays from the lamp filament F are reflected downwardly andinwardly as indicated at the left of Figure 1. The paths of rays 35, 36and 37 falling on the sides of the reflector and of reflected rays 35',36 and 37' in the plane 11 of Figure 2 are shown in full lines, whiletypical direct and reflected rays in the diagonal plane are indicated bydotted lines 38, 38'. Similar ray paths 39, 39' and 40, 40' areindicated in Figure 1a. Similar actions take place in all azimuths withthe result that the dominant reflected light proceeds downwardly asthough coming from virtual sources in an annular region above thereflector. This light is at relatively low angles from the nadir. Thedirect light above the source is reflected close to the filament asindicated at 41, 41'.

The reflected light, as well as the direct light, which escapes belowthe reflector, is refractively transmitted downwardly through a lensplate or refractor 50, the details of which will be discussed below. Thereflected rays 35' to 40, inclusive, are beyond the normals to therefractor surface and are deviated as indicated at 35" to 40",inclusive, so as to be emitted at higher angles from the nadir. Theangles of incidence of reflected light on the upper surface of therefractor 50 are, especially at the margins and corners of therefractor, less than with a flat refractor, so that more eflicientshallow prisms on the lower surface are effective in obtaining thedeviation desired. The direct rays, such as full line rays 51, 52, 53and 54 (in place 1-1) and dotted line rays 55, 56. and 57 (in thediagonal plane) are emitted less divergently as indicated by rays 51" to57". The reflected rays emitted from any point on the surface haveapproximately the same vertical angles as the direct light refractivelytransmitted, so that .the dominant light control is approximately thatof Ralph Patent No. 2,101,199, dated December 7, 1937.

In the present construction, the reflected light has relatively lowangles of incidence on both surfaces and these rays are raised slightly.For the direct light, however, the angles of incidence on both surfacesare greater and the direct rays are lowered to a greater extent. Owingto the steepness of the marginal portions of the plate, the angles ofincidence for the higher rays approach 90 so that the portion of lightreflected at the incident surfaces becomes, very high and the portion oflight accepted correspondingly reduced. As less light is accepted atthese high angles of incidence, less light is transmitted and lowerbrightness brought about. Most of the deviation takes place at the uppersurfaces. The shallow prisms make it possible to reduce interception andloses of intermediate surfaces.

The present invention relates to improvements over the showings of theRolph patent mentioned, whereby the brightness characteristics andappearance of the luminaire, whether lighted or not, and the eificiencyof the luminaire are greatly improved. While the refractor of thatpatent is flat, and flat refracting plates are commonly used, the squarelens plate or refractor 50, as shown in Figures 1 to 9, inclusive, is ofupwardly convex or dome section and all four side edges of the refractorare in a common plane. When one views a plate of such profile at anglesfar from the nadir, the'nearer edge of 4 Outside the circle 62 and'belowthe line 62' are shown a series of closed figures or loops 63, 64, 65and 66 and iso-elevational lines 63", 64", 65", 66". Each of these loopsis made up of four short radius arcs 63a to 66a,

the plate eclipses the nearer portion of the plate so that the areaobserved is. much less than that of a flat plate of the same size. Thisis indicated by the sight lines 58, Figure 1. The screening angle 59 forthe. center of the lens is. approximately 15,".

In order that the under surface of the platethe side toward the observershould be continuously concave in all directions, the profiles, of theplate vary from the center of the sides to the corners and 'at the same.time horizontal curvatures are secured throughout the lens areas. Thisavoids mitres.

To generate a refractor form for this purpose, onefirst selects theprofile at the center and parallel with the sides. A suitable profilefor the lower surface is indicated at 60., Figure 7.. While it may beflat at thecenter, it is preferably slightly convex upwardly. The sidesare steeper as is apparent from the drawing. In: order that the entireplate, receive direct light from the source, the steepness is limited toan amount such that direct light can. be transmitted. The extremedirectrays are indicated in 54 and: 57, Figure la. The shapeof the loweror light emergentsurface of the glass. plate is determined by theplunger used in the molding apparatus. To pro-. duce the proper profileon the plunger in all azimuths, itis first given the selected profile inthe four principal directions; The central portion, out to the circle62,.-is asurface of revolution about the; axis, 61,. as; indicated byradius 62' and by iso-elevational line 62",.Figure 7.;

inclusive, and four long radius arcs 63b to 66b, inclusive. The pointsof contingency of these arcs are along the dotted lines 67. Theoutermost loop approaches the square shape.

The lower surface of refractor 50 has concentric refracting prismsgenerally numbered 70. These prisms, however, are not of uniformrefracting power and elevation above the refractor flange in allazimuths, except Where the refractor form is surface of revolution. Theprisms in this central region are thus indicated in Figures 4 and 5inside prism 70a.

The prism profile from center 61 to the side edges of .the plate isrepresented by the regressed line 71, Fig- .ure 5, while that from thecenter to the corner is represented by similar line 72. Prism outlinesof like radii are one above the other in this figure. The profiles ofthe opposed incident surfaces are shown by dotted lines 73 and 74,Figure 5. At the increased radius, the incident surface opposite a prismof particular radius varies from a minimum toward the corners of theplate to a maximum toward the side edges. To compensate for this, thefaces of the emergent prisms beyond about prism 70a vary according tothe angular distance from the radius to the center of the sides of therefractor. Heavy dash lines 75 and 76 in Figure 4 show where the prismslope changes as one passes about the faces of the circular prisms.Between the line 75, 75 at the corners, the profile is that shown at 72,While between the line 76 in one quadrant and a similar line 76 in anadjacent quadrant, the profile isthat of 71. The prisms in profile 71are deeper than those in profile. 72. At the orientation of profile 71,a prism such as 70b is located considerably lower vertically and is ofgreater width w than is the-same prism at the orientation of profile72,. where it is higher and .of narrower width w. Between the lines 75and 76 the slope is, intermediate the other slopes.

Figure 8 shows the regressedprisms 70 at a large scale. The surfaces 73and 77 are at the proper angle to achieve the desired. deviation of thedirect light. The riser or so-called inactive surface is at 78 and inpractice, the surfaces 77 and 78 are always connected by the roundedsurfaces 79, 79. In this present optical design the active surface isextended back of the limited refracted ray 30 nthe glass retractingmedium so that there is a small part of the. prism at the corner whichis eclipsed by the root of the next prism. This eclipsed region isindicated by dotted area in Figure 8. None-of the dominant rays fall 1n.this region so that light scattering by the rounded area 79 causing highangle brightness is avoided.

The arrangement of Figure 8 contrasts very favorably Wlth constructionsusually employed where the slope of the riser is parallel with the rayin the glass. As shownin Figure 8a, such rays as 82, fall on thecorresponding rounded surface and are scattered as indicated at 83 toproduce high angled light. This light leakage is always stronger ,on thenear side of the plate toward the observer than on the far side, so thatit tends to buildup brightness. Owing to the curvature ofthe lowersurface of the lens In all directions, the concentric .lens prismsappearing as circles in Figure 4 become distorted when viewed .ob'llquely. The. rise and fall of the prisms relative to the flange of thelens is illustrated in Figures 9'and 9a.

The above discussion has assumed that the upper surface of therefracting plate is smooth. For incandescent sources, it isdesirable toprovide the lensplate with diflusion means whichscatters the lightcircumferentially, so-that the. plate presents a betterlightedappearance and the reflector and lamp areobscuredfrom directobservation.

Thepresent. construction. provides an. improved diffusiontmeans for.thisxpurpose. Lateral..-deviati on-: for..diffua sion purposes istypically obtained by radial flutes. As the width of the true radialflutes narrows towards center, such flutes do not provide the mostefiicient diffusion.

The new flute layout is illustrated herein in Figures 2, 3, 3a and 3b.The square upper surface of the refractor is divided into subordinaterectangular areas by narrow smooth strips which cross at the center andare parallel with the edges of the plate. These strips are indicated at90. The small square disconnected or discrete blocks of areas 91 betweenthese strips are provided with diffusing flutes. In each square area,one of the flutes marked r is radial, and all of the others are parallelwith this flute. The flutes are preferably convex and of identicalcrosssection, and contiguous. To produce them the mold surface is cutaway by a cutter of appropriate contour which traverses the desired areaof the mold for each flute. If desired, the ones near the center of theplate may have greater diffusing power than those near the edges of theplate.

As the groups of flutes in areas 91 occupy varying azimuth anglesdepending upon their location over the surface of the plates, theextreme flutes in the respective areas do not all have the sameinclination to the radial plane through the same. For example, theradial plane 92a makes, with the direction of the flute 92b, an anglesuch as 92c, and the radial planes 93a and 94a make smaller angles 93cand 94c, respectively, with the direction of the flutes 93b and 94b.Thus, over each area there is a symmetric diffusion from the radialflute r and asymmetric diffusion of increasing amount and opposite signeach side of the radial flute. It is greater near the center of theplate where there is a tendency to produce a hot spot owing to thecloseness of the light source. This arrangement serves to effect anall-over circumferential diffusion which provides even brightness and asmooth lighting pattern. The flutes will be visible through therefractor.

The adoption of the improved construction above set forth has made itpossible to substantially increase the output of light from suchlighting fixtures and improve utheir appearance whether lighted or not.For example, a square 300 watt fixture, made with reflector and flat re-;fractor shown in Rolph Patent 2,101,199, December 7, .1937, with thediffusion pattern of Rolph Patent 2,099,034, dated November 16, 1937,has a 045 output of about 40.8%, and a 0-60 output of about 50.1%, whilea square fixture with the same input and adapted to fit in the sameplaster flange as the former square fixture, but having the reflectorand refractor shown herein, has at corresponding angles outputs of about56.4% and 61.6%, respectively. Per-centagewise, the improvement is about38% in the more significant 0-45" zone and 23% in the 0-60 zone. Also alarge part of the nearer portions of the concave lens surface isscreened against observation at wide angles from the nadir. For example,at 15 below the horizontal there is only about one-third as muchprojected area on the near side as with a flat lens of the same size,and this is lateral of the center line. As much of the high angledscattered light from a lens comes inherently from the near side, thereduction in projected area substantially reduces brightness at highangles from the nadir.

It, will be understood that one can utilize the concave lens plateprofile in a round construction with a round reflector, in which casethe full line showing or the dotted line showing of Figure 1 may besections on surfaces of revolution. The upper surface of such roundplate may have a similar diffusion pattern and in the lower surface theprisms are annular and horizontal instead of having a rising andlowering contour. The diffusion pattern on the top of the lens plate maybe radially employed on a flat plate. The grooves are easily cut on theflat surface of the mold, or plunger.

The concave lens is also suitable for use with any fluorescent lightsources. For such fixtures, the reflectors would be inverted troughs ofsuitable profile above the sources to handle the light from such sourcesand the refracting plates would have a profile similar to that of Figure1 with suitable rectilinear prisms, except for the retracting prisms atthe ends. These end plates shown at 100 in Figure 10, would have somerectilinear prisms 101 and at the end would have the same contour asonehalf of the plate 50, and generally indicated at prisms 102. Theupper surface for the fluorescent luminaire plate may be smooth.

Figure 11 shows a lens similar to the lens above described, except thatat a distance from the center, the prisms instead of being concentricover the entire surface of the lens are closed loops with parallelportions 111, parallel with the sides of the plate and connecting arcs112. If such an arrangement of prisms were cut on a refractor form suchas in Figures 6 and 7, the arcs 112 would well be about the same centersas arcs 63a etc., and the parallel portions would be arched. For such anarrangement of straight and curved loop prisms it would be easier toprepare the refractor form with surfaces of simple curvature betweendiverging lines 67, 67 of Figure 7. The over-all output and lightpattern of the luminaire with non-concentric prisms would be almostidentical as would be the shielding action, but the appearance would bealtered.

What is claimed is:

l. A direct lighting luminaire comprising a light source, an openmouthed specular reflector about the light source with its vertical axisof symmetry through the source and having its mouth substantially 40below the horizontal through the source and a profile to convergereflected light toward the axis at relatively steep angles, a prismaticplate across the mouth of the reflector to intercept direct andreflected light and having regressed, light-deviating prisms on thelower surface to deviate the light with respect to said vertical axis,the margins of the prismatic plate being close to the margins of thereflector and having an upper face generally convex in transverse planesand of a steepness to be substantially in line with the source so thatthe angles of incidence of the most divergent direct rays approach withconsequent reduced acceptance and transmission and. the reflected raysfalling thereon are adjacent the normals t0 the surface, and on the sidetoward the vertical axis, the lower surfaces of the prisms in transverseplanes being at outwardly acute angles with respect to the opposed uppersurfaces, whereby divergent direct light is transmitted with reduceddivergence and the convergent reflected light is transmitted withgreater convergence, but with less deviation in passing through theplate than the direct light.

2. The direct lighting luminaire of claim 1, wherein the source is asubstantially point source, and the reflector and prismatic plate acceptlight in all azimuths and redirect the light radially.

3. The direct lighting luminaire of claim 1, wherein the source is asusbtantially point source, and the reflector and prismatic plate acceptlight in all azimuths and redirect the light radially, and wherein theupper surface of the prismatic plate has a light diffusion patternacting to spread the light circumferentially and formed of discreteareas of parallel flutes, one flute in each area being radial.

4. The direct lighting luminaire of claim 1, wherein the source is asubstantially point source, and the reflector and prismatic plate acceptlight in all-azimuths and redirect the light radially, and wherein therisers intermediate the active faces of the regressed prism are steeperthan the limiting ray in the plate so that the lower or outside cornerof the prism is eclipsed by the upper or inside corner of the prism.

S. The direct lighting luminaire of claim 1, wherein the source is asubstantially point source, the reflector is square with a square mouthand redirects the reflected 7 light radially inward, the retractingplate is square and of less marginal steepness radially at the cornersthan at the center of the sides, and the prisms are disposed about thecenter to redirect the direct and reflected rays radially.

6. A direct lighting luminaire such as claimed in claim 5, wherein theretracting power of the prisms is greater at the corners of the platethan at the centers of the sides whereby the higher angle direct lightfalling on the corners is deviated more than that received between thecorners.

7. A direct lighting luminaire such as claimed in claim 1, wherein themargins of the retracting plate are subtantially 15 below the horizontalthrough the center of the prismatic plate so as to eclipse the centralnear side of the plate at angles of observation about 75 above the nadirand substantially reduce the visible projected area of the near sidevisible in regions beyond the highest direct and reflected rays emittedby the plate.

8. A direct lighting luminaire comprising .a light source, a reflectorsymmetrical about a vertical plane through the source and of a contourabove substantially 40 below the horizontal to reflect rays downwardlyand convergently toward said plane, and a retracting plate having on thelowersurface and on opposite sides of said plane retracting prisms whichincrease the convergence of the emitted reflected light and alsodecrease the divergence of the emitted direct light, the plate beingdownwardly concave with its center substantially horizontal and itsmargins steeply curved in an amount to make the marginal reflected lightapproximately normal to thereby effect high utilization of the reflectedlight falling thereon, and tohave high angles of incidence of nearly 90for direct light to reduce acceptance thereof and transmission therebyand to screen the near side of the plate against observation at highangles from the nadir.

9. A direct light lum'inaire such as claimed in claim 8, wherein thesource is substantially a point source, the prisms on the retractingplate are disposed about a vertical axis through the source and theupper surface of the plate is provided with discrete areas made up ofparallel flutes all of equal retracting power, one flute in each areabeing radial so that the others are oblique to the radius wherebydiffusion in regions near the center of the plate is greater than in theouter regions to thereby reduce the brightness of the center of theplate near the source.

[10. A retractor form of polygonal shape'and having opposed coplanarmarginal edge portions and its opposite surfaces between the edgeportions continuously concave toward the plane of the edge portions, theintersections of said surfaces with plane's parallel with saidedge-plane and approaching them being circles of increasing radius abouta center surrounded :by closed figures composed of circular arcs, thearcs between the center and the corners of the polygon having lesseningradii toward the corners, the arcs between the center and the sides ofthe polygon having. increasing radii so that the successive closedfigures approach the polygonal outline.

11. In combination, a substantially point light source, a substantiallysquare ,light retracting and transmitting plate intercepting directlight rays in a region with the source as its apex, the plate having anupwardly ,convex light incident surface substantially flat centrally andof steepness at the margins to be substantially coincident with theoutermost rays in the said region, .whereby the incident light isretractively transmitted wih .the maximum deviation into the plate, thelower surface of the plate having light condensing prisms which reducethe divergence of the direct light, the central prisms having uniformretracting power-inall azimuths, the outer prisms in the cornerportions-of the p1ate.having;more retracting power than prisms atcorresponding radii toward the-side edgesof the plate.

12. Alight transmittingand diffusing. refractor having on ne f ce serieo ligh convergin prisms disposed about a center and on the other facediscrete diffusing areas separated by smooth areas and wherein thediffusing areas are each made up of a series of parallel diffusingflutes, one medially disposed flute in each area being radial so thatthe diffusion, while generally transverse of the bending of the rays bythe prisms, varies in direction over each diffusing area. '13. A lighttransmitting and diffusing refractor having on one face a series oflight converging prisms disposed about a center and on the other face aseries of narrow smooth areas at right angles to one another andseparate rectangular areas each made up of narrow flutes parallel withone another on each such area, one medially disposed flute in each areabeing radial so that the diffuser, whilegenerally transverse ot thebending of the rays by the prisms varies in direction over each diffuserarea, all the diffusing flutes being of like retracting power so thatthere is greater variation in direction of diffusion in thefluted areasnear said center than in the more remote areas.

14. A light transmitter and diffuser made of transparent material andhaving a relatively large, continuous light receiving area made up ofrelatively narrow smooth areas and relatively large diffusion areasseparated from one another by the smooth areas, and wherein the separatediffusion areas are each made up of relatively narrow flutes parallelwith one another on such diffusion area and in generally radialdirections from a point located cent-rally of the light receiving areaso that the light isdiffused in tangential directions.

15. A light transmitter and diffuser such as claimed in claim 14 whereinthe smooth areas are straight strips at right angles to one another andthe diffusion areas are rectangular.

16. A light transmitter and diffuser such as claimed in claim 14,wherein one flute in each fluted area is in a plane radial with respectto an axis normal .to the entire light receiving area so that light isdiffused by the flutes in each area in variant directions with respectto the radial. planeof the radial flute thereof.

17. A light transmitter and diffuser such as claimed in claim 14,wherein the flutes in each area are adjacent one another.

18. A light transmitter and diffusersuch as claimed in claim 14,.wherein all the flutes in all the areas are of like retracting power.

19. A direct lighting luminaire comprising a light source, a reflectorsymmetrical about a vertical median plane through the source extendingbelow the source and. of a profile to reflect light downwardly towardsaid median plane and a retracting plate having on its lower faceconcentric prisms which increase the convergence .of the reflected raysand reduce the divergenceof the direct rays falling on the plate, the,plate also having relatively steep upwardly converging rnarginalportions under the marginal portions of the reflector with angles ofincidence for direct light approaching 90 whereby the direct lightaccepted by the marginal portions is reduced, the plate also beingrelatively flat inside the steep portions so that at high angles ofobservationhelow the horizontal normal to said median plane the nearside edge of the plate screens the nearer areas of the .plate from Wh Ph,,the small portion of the highest angled direct lightaccepted is beingemitted.

.20. A refractor comprising a substantially square light refracting andtransmitting plate having an upwardly convex light incident surfacewhich is substantially flat centrally and of appreciable steepnessbetween the central portion .and the edgesvof the plate, said platehaving alower light emitting surface which is generally concave, saidlower surface having regressed condensing prisms, the prisms bcz'ngintheform of circles of increasing radius about the center of the .platetmdcircular arcs betweenthe center and the comers of the plate, the uppersurface ;:being;,a.Jtghtdifiusing surface .made upbfrelatively narrowsmooth areas and relatively large diffusion areas separated from oneanother by the smooth areas, and wherein the separate diffusion areasare. each made up of relatively narrow flutes parallel with one anotheron such difiusion area and in generally radial directions from thecenter of the plate so that thelight'is diffused in tangentialdirections. I g

21. A refractor comprising a prismatic plate of square shape and havingopposed coplanar marginal edges, said plate ha ving an upper lightincident generally convex surface between the edge portions and a lowergenerally concave surface between the edge portions, the marginal edgesof the refracting plate being substantially 15 below the horizontalthrough the center of the prismatic plate so as to eclipse the centralnear side of the plate at angles of observation about 75 above thenadir, said plate'having on its concave surface regressed lightcondensing prisms with relatively narrow risers and relatively wideactive surfaces, said prisms being in the form of circles of increasingradius about the center of the plate and circular arcs between thecenter and the corners of the square.

22. A direct lighting luminaire comprising a light source, an openmouthed specular reflector about the light source having a vertical axisof symmetry through the source and having its mouth substantially 40below the horizontal through the source and a profile to convergereflected light toward the axis at relatively steep angles, a prismaticplate across the mouth of the reflector to intercept direct andreflected light, the margins of the prismatic plate being close to themargins of the reflector, said plate being of rectangular shape andhaving opposed coplanar marginal edge portions, said plate having anupper generally convex light incident surface constituting the entireupper surface between the edge portions and a lower generally concavesurface constituting the entire lower surface between the edge portions,said plate. having on its concave surface regressed light convergingprisms with relatively narrow risers and relatively wide activesurfaces, said prisms being in the form of closed figures includingcircular arcs concave toward the center of the plate and extendingsymmetrically about lines bisecting the corners of the plate andstraight lines parallel to the edges of the plate joining the ends ofthe arcs.

23. A refractor comprising a prismatic plate of polygonal shape andhaving opposed coplanar marginal edge portions, said plate having anupper light incident generally convex surface between the edge portionsand a lower generally concave surface between the edge portions, saidplate having on its concave surface regressed light condensing prismswith relatively narrow risers and relatively wide active surfaces, saidprisms being in the form of circles of increasing radius about a centerand surrounded by closed figures, said closed figures including circulararcs between the. center and the corners of the polygon, the portions ofthe outer closed figures between the center and the sides of the polygonbeing substantially parallel to the sides of the polygon.

24. A refractor comprising a prismatic plate. of polygonal shape andhaving opposed coplanar marginal edge portions, said plate having anupper generally convex light incident surface between the edge portionsand a lower generally concave surface between the edge portions, saidplate having on its concave surface regressed light converging prismswith relatively narrow risers and relatively wide active surfaces, saidprism being in the form of circles of increasing radius about a centerand surrounded by closed figures, said closed figures including circulararcs between the center and the corners of the polygon, said arcs havinglessening radii towards the corners, the portions of the outer closedfigures between the center and the sides of the polygon beingsubstantially parallel to the sides of the polygon.

25. A refractor comprising a prismatic plate of polygonal shape andhaving opposed coplanar marginal edge portions, said plate having anupper light incident gen? erally convex surface. between the edgeportions and a lower generally concave surface between the edgeportions, said plate having on its concave surface regressed lightcondensing prisms with relatively narrow risers and relatively wideactive surfaces, said prisms being in the form of circles of increasingradius about a center and surrounded by closed figures, said closedfigures including circular arcs between the center and the corners ofthe polygon, said arcs having lessening radii toward the corners, theportions of the outer closed figures between the center and the sides ofthe polygon being substantially parallel to the sides of the polygon,said upper surface being a light difiusing surface.

26. A refractor comprising a substantially square light refracting andtransmitting plate having an upwardly convex light incident surfacewhich is substantially flat centrally and inclined between the centralportion and the edges of the plate, said plate having a lower lightemitting surface which is generally concave, said lower surface havingregressed condensing prisms, some of said prisms being in the form ofcircles of increasing radius about the center of the plate, theremainder of said prisms being in the form of closed figures surroundingthe circles, the closed figures including circular arcs between thecenter and the corners of the plate, said arcs having lessening radiitoward the corners the portions of the outer closed figures between thecenter and the sides of the plate being substantially parallel to thesides of the plate.

27. A refractor comprising a substantially square light refracting andtransmitting plate having an upwardly convex light incident surfacewhich is substantially flat centrally and inclined between the centralportion and the edges of the plate, said plate having a lower lightemitting surface which is generally concave, said lower surface havingregressed condensing prisms, the prisms being in the form of circles ofincreasing radius about the center of the plate and closed figuressurrounding the circles, the closed figures including circular arcsbetween the center and the corners of the plate, said arcs havinglessening radii toward the corners, the portions of the outer closedfigures between the center and the sides of the plate beingsubstantially straight lines, said upper surface being a light difiusingsurface.

28. A refractor comprising a prismatic plate having a marginal edgeportion lying in a single plane, said plate having an upper lightincident generally convex surface and a lower generally concave surface,said plate having on its concave surface regressed light condensingprisms with relatively narrow risers and relatively wide activesurfaces, a plurality of said prisms being in the form of circles ofincreasing radius about a center, said upper surface being a lightdifiusing surface the risers intermediate the active faces of theregressed prisms being steeper than the limiting ray in the plate sothat the lower or outside corner of a prism is eclipsed by the upper orinside corner of the prism.

29. A direct lighting lum-inaire comprising a light source, an openmouthed specular reflector about the light source having a vertical axisof symmetry through the source and having its mouth substantially 40below the horizontal through the source and a profile to convergereflected light toward the axis at relatively steep angles, a prismaticplate across the mouth of the reflector to intercept direct andreflected light, the margins of the prismatic plate being close to themargins of the reflector, said plate having a marginal edge portionlying in a single plane, said plate having an upper light incidentgenerally convex surface and a lower generally concave surface, saidplate having on its concave surface regressed light condensing prismswith relatively narrow risers and relatively wide active surfaces, aplurality of said prisms being in the form of circles of increasingradius about a center, said upper surface being a light diffusingsurface, the risers intermediate the active faces

